Electrophotographic process utilizing single charging means for effecting simultaneous functions of charging and facilitating toner image transfer

ABSTRACT

The electrophotographic duplication process comprising: A. CHARGING THE SURFACE OF AN ELECTROPHOTOGRAPHIC PHOTORECEPTOR; B. EXPOSURE SAID CHARGED SURFACE TO FORM AN ELECTROSTATIC ALLY CHARGED LATENT IMAGE THEREON; C. DEVELOP SAID LATENT IMAGE WITH A TONER HAVING A CHARGE OPPOSITE TO THAT OF SAID LATENT IMAGE; D. CHARGING SAID DEVELOPED LATENT IMAGE AND SAID PHOTORECEPTOR WITH A CHARGE OF THE SAME POLARITY AS IN STEP (A), THEREBY REVERSING THE POLARITY OF SAID TONER AND RECHARGING SAID PHOTORECEPTOR SURFACE; E. TRANSFERING THE MAJORITY OF SAID TONER TO A RECEIVING LAYER TO FORM A TONER IMAGE; F. REMOVING RESIDUAL TONER; G. REPEATING (B) - (F). Apparatus to accomplish the above purpore requiring only one corotron.

United States Patent 1 Obuchi [4 1 Oct. 9, 1973 ELECTROPHOTOGRAPHIC PROCESS UTILIZING SINGLE CHARGING MEANS FOR EFFECTING SIMULTANEOUS FUNCTIONS OF CHARGING AND FACILITATING TONER IMAGE TRANSFER [75] Inventor: Kazuo Obuchi, Odawara-shi,

Kanagawa, Japan [73] Assignee: Fuji Photo Film Co., Ltd., Minami- Ashigara-Shi, Kanagawa, Japan 22 Filed: Dec. 10, 1971 211 App]. No.; 206,034

[30] Foreign Application Priority Data Dec. 10, 1970 Japan 45/109878 [52] U.S. CI 355/3, 96/1.4, 117/37 LE, 355/17 [51] Int. Cl G03g 15/00 [58] Field of Search 355/3, 16, 17; 96/l.4; 117/37 LE [56] References Cited UNITED STATES PATENTS 3,041,167 6/1962 Blakney et a1. 96/l.4 2,817,765 12/1957 Hayford et a1 3,368,894 2/1968 Matkan et al 117/37 LE Primary Examiner-Richard L. Moses Attorney-Gerald J. Ferguson, Jr. et a1.

[57] ABSTRACT The electrophotographic duplication process comprising:

a. charging the surface of an electrophotographic photoreceptor;

b. exposure said charged surface to form an electrostatic ally charged latent image thereon;

c. develop said latent image with a toner having a charge opposite to that of said latent image;

(1. charging said developed latent image and said photoreceptor with a charge of the same polarity as in step (a), thereby reversing the polarity of said toner and recharging said photoreceptor surface;

e. transfering the majority of said toner to a receiving layer to form a toner image;

f. removing residual toner;

g. repeating (b) (f).

Apparatus to accomplish the above purpore requiring only one corotron.

3 Claims, 7 Drawing Figures ELECTROPI-IOTOGRAPHIC PROCESS UTILIZING SINGLE CHARGING MEANS FOR EFFECTING SIMULTANEOUS FUNCTIONS OF CHARGING AND FACILITATING TONER IMAGE TRANSFER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic duplicating process.

2. Description of the Prior Art Up to now, known devices for effecting electrophotographic duplicating employing a photoreceptor for repetitive use and involving an image transferring step have been rather complicated, and consequently have been large in size and have involved comparatively high manufacturing costs.

A typical example of such conventional electrophotographic duplicating process is shown in FIG. 1. A cylindrical photoreceptor I is first given an electrostatic charge by a charging corotron 2 of a polarity determined by the physical properties of the photoreceptor used while rotating in the direction of the arrow shown in FIG. 1. The surface of photoreceptor is then subjected to exposure represented by 12 through an optical system not shown in the drawing.

An electrostatic latent image is formed in a known manner on the surface of photoreceptor by the exposure. This electrostatic image is developed when it passes developing device 3, and a transferable image corresponding to the electrostatic latent image is formed.

Ordinarily, the image is formed by the application of a fine colored plastic powder known as a toner. As for developing, known electrophotographic developing process, such as cascade developing magnetic brush developing and the like are typically used.

The image formed on the surface of photoreceptor 1 is brought into intimate contact with a receiving material 4, which is conveyed at the same speed as the surface of photoreceptor l, and is transferred onto the surface of the receiving material 4, for example, by the known electrostatic transferring process, which involves providing the back surface of receiving material 4 with'an electrostatic charge opposite polarity to that of the electrostatic charge on the image-forming substance (e.g., the toner). This is accomplished by means of transferring corotron 5 disposed at the back surface of the transfer material facing to the photoreceptor I.

By this transfer step, almost all of the toner is transferred to the receiving material, but a part of the toner remains on the surface of the photoreceptor, and it is necessary to clean the surface of the photoreceptor when it is used repeatedly. This is typically accomplished in the manner described below.

First, by a charge is provided to the photoreceptor 1 (which has been subjected to the transferring process) from a corotron 6 which erases the electrostatic charge, whereby the major portion of the residual electrostatic charge is neutralized and the electrostatic attraction between the photoreceptor l and residual image-forming substance is attenuated. Then, the remaining image-forming substance is mechanically cleaned by a cleaning means, such as rotary brush 7.

Finally, a sufficient quantity of exposure from light source 8 is given the photoreceptor l to erase the residual electrostatic charge remaining thereon, whereby the photoreceptor l is restored to its initial state and repeatedly reused.

As is seen from the above description, complicated steps are needed for conventional electrophotographic duplicating processes, and a number of complecated elements are necessary when a device for effecting such process is to be constructed.

For instance, it is to be especially noted that conventional processes and apparatus require a supply of high voltage, that is, as many as 3 corotrons are required in the process. This is not desirable from the viewpoint of complexity of the device and also from the viewpoint of economy, when considering the fact that it is required to have a control device for a high voltage electric source that can separately adjust the voltage because the voltages which are applied to the three corotrons should be different for each one.

SUMMARY OF THE INVENTION After a first charging to one polarity and exposure and development of an electrostatic latent image with a toner having a polarity opposite that of the first charging, if the underlying photoreceptor is charged to the same polarity as in the first charging, the polarity of the toner is reversed, and the photoreceptor recharged, whereby after toner image transfer to a receiving layer and optional removal of rendered toner, the photoreceptor may be immediately exposed, developed, etc., without an initial charging. Apparatus to accomplish the above needs only one corotron.

Compared with known electrophotographic duplicating processes, the process of the present invention can be carried out with less steps, and the construction of the electrophotographic duplicator can be remarkably simplified, as seen in FIG. 3.

The object of the present invention is to provide a process for and particularly an electrophotographic duplicating process employing a photoreceptor for repetitive use and accompanied by an image-transferring step, in which processing steps are reduced, the device to be used is more simple in its'construction, and can be manufactured in small sized device with lower costs, compared to conventional duplicating processes which have been put in practice or published heretofore.

Brief Description of the Drawings FIG. 1 is a diagram illustrating a known electrophotographic duplicator.

FIG. 2 is a diagram illustrating an electrophotographic process according to the present invention.

FIG. 3 is a diagram illustrating an electrophotographic duplicator for effecting the process according to the present invention.

Detailed Description of the Invention The steps of the electrophotographic duplicating process according to the present invention will now be described with reference to FIG. 2.

In FIG. 2a, a photoreceptor ll (herein shown as a flat plate-like photoreceptor for convenience of illustration) is given a uniform electrostatic charge from a corotron 9. In the drawing, the electrostatic charge given is shown as a positive charge a negative charge could also be used depending on the physical properties of the photoreceptor, as is known to the art.

In FIG. 2b, by giving an exposure 12, in the form of an image, onto the surface of the charged photoreceptor body 11, an electrostatic latent image corresponding to the light and dark portions of the image is obtained.

In FIG. is shown the state in which the abovementioned electrostatic latent image is developed by a known electrophotographic developing process, and an image 13 is formed of a toner. In a normal positive image, the toner image 13 has an electrostatic charge of a polarity opposite to that which is given to the photoreceptor 11.

In FIG. 2d, the surface of the photoreceptor 11 on which toner image 13 is formed is charged with the same polarity as in case of the process shown in FIG. 2a from a corotron 9, in this embodiment a positive charge at this time the polarity of the toner which forms the image 13 is reversed, and simultaneously the portions of the photosensitive plate that lost their electric charge by exposure are recharged. In this case, the portion of the photoreceptor covered by toner image 13 is also recharged through gaps which exist among the toner particles. The residual electrostatic charge on this portion (under the toner 13) is more attenuated than in the state shown in FIG. 20 by dark decay of the photoreceptor. However, compared with the potential of the photoreceptor in non-image partion, the potential is high.

The following material explains step 2d and relates to uniformly charging the surface of the photoreceptor with reversing the toner image polarity, thereby preparing the toner image for the following transferring step 22. For the case when the photoreceptor is charged in a uniform condition, if the potential of the photoreceptor rises in proportion to the electrostatic charge given, the potential of the toner image portion and the nonimage portion must both rise, maintaining the potential difference that both portions had immediately before the process shown in FIG. 2d. However, in practice, because of the saturation potential, which is determined by the electrostatic charging condition, no significant difference exists between the potential toner image portion and the non-image portion of the photoreceptor at the completion of the electrostatic charging step.

In addition, because of the existence of a shielding effect to the flow of electrostatic charge due to the toner particles in the toner image portion, it is possible to uniformly recharge the surface of the photoreceptor 11 by appropriately selecting the charging conditions regardless of the existence or non-existence of toner image.

In FIG. 2e, a receiving material 4 is superposed on the surface of the photoreceptor, pressed from the back side by, for example, a grounded conductive roller 10, and an image 13 is transferred onto the surface of receiving material. The residual toner image is then cleaned off the photoreceptor 11 while maintaining the latter in a dark place. The photoreceptor, being already uniformly charged due to the process shown in FIG. 2d, can be immediately returned to the step shown in FIG. 2d and processed repeatedly in the manner as described above.

It is further to be added that, because an electrostatic charge of the same polarity is given to the toner and the photoreceptor in FIG. 2d, a repulsive force acts between the toner and the photoreceptor and thereby the execution of the cleaning step is easy. Accordingly, the existence of the corotron 6 for erasing a charge as shown in FIG. 1 becomes unnecessary.

Further, from the second processing cycle on, the electrostatic latent image is formed by utilizing the charge given in the process step shown in FIG. 2d, and thus the light source for erasure 8 as shown in FIG. 1 is not needed at all.

Furthermore, according to the process described above, in the case when a photoreceptor of endless construction, such as a cylindrical or belt-like body, is repetitively used, the same corotron is used for corotron 9 in the process step shown in FIG. 2a and 2d, serving simultaneously as corotoron 2 and 5 shown in FIG. 1. As a result, one corotron will be enough to meet the needs of the process of the present invention.

FIG. 3 shows an example of a device in which the electrophotographic duplicating process according to the present invention can be repetitively effected using a cylindrical photoreceptor.

In the device shown in FIG. 3, the cylindrical photoreceptor 1 is first given an electrostatic charge from coroton 9 while rotating in the direction of the arrow. Then, an exposure 12 is given to its surface through an optical system not shown in the drawing. The electrostatic latent image formed by exposure is developed when it passes through developing device 3, and a transferable image is thereby formed. Developing processes and developers heretofore used by the prior art in known electrophotographic duplicating processes may be employed.

The image is then reversed in polarity of electrostatic charge by means of corotron 9 and the photoreceptor 1 also is restored with the electrostatic charge which it lost by exposure.

The image is then brought into contact with the receiving material 4 conveyed at a speed corresponding to the surface speed of the photoreceptor I, pressed from the back by means of grounded conductive transfer roller 10 and transferred onto the surface of receiving material 4.

The remaining image-forming substance which has not been transferred is removed by cleaning means 7, which may be a rotating brush, and the photoreceptor 1 is subjected again to the above-mentioned process starting from the exposure step. In this device, it is naturally unnecessary to effect the transferring and cleaning steps after the first electric charging has been effected in the first one rotation, although these steps does not constitute any obstacle if effected formally.

Further, this being evident from the nature of the process according to the present invention, any process step which would extraordinarily lower the electrostatic charge of the surface of photoreceptor can not be adopted.

It is to be noted in FIG. 2d, that the center of the layer would not have a lower charge than the other portions because the portion of the photoreceptor covered by toner image 13 is also recharged through gaps which exist between the toner particles.

Accordingly, in practice, because of the saturation potential, no significant difference exists between the potential of the toner image covered portion and the non-image portion of the photoreceptor at the final period of the electrostatic charging step. i

In addition, because of the existence of a shielding effect to the flow of electrostatic charge due to the toner particles in the toner image partion, it is possible to uniformly recharge the surface of the photoreceptor 11 by appropriately selecting the charging conditions regardless of the existence or non-existence of the toner image.

In a device as shown in FlG. 3 a description was given of the case where a grounded conductive roller 11 was used in the transfer step. [t is also possible to apply a bias of opposite polarity to that of the electrostatic charge the image has to the transfer roller, in conformity with the known transferring process using a biased roller.

Further, as for the means for pressing the receiving material onto the surface of the photoreceptor in the transfer step, it is not necessary to use a roller, and an element such as slider may also act in an excellent manner. In addition, where the receiving material has conductive layer, this roller or slider need not always'be conductive.

What is claimed is:

1. ln electrophotographic duplicating apparatus comprising a photoreceptor surface, charging means to charge said surface, exposing means to expose said charged surface, developing means to develop said charged surface and provide a toner image and toner image transfer means for transferring said toner image to a receiving material, the improvement wherein said toner transfer means is disposed immediately after said charging means, said charging means effecting the simultaneous functions of charging said photoreceptor and reversing the polarity of said toner image from an initial value, which initial value is opposite to the charge imparted by the charging means.

2. The improvement as in claim 1 where there is only one said charging means.

3. Electrophotographic duplication apparatus comprising:

means for charging the surface of an electrophotographic photoreceptor; means for exposing the charged surface to form an electrostatically charged latent image thereon; means for developing said latent image with a toner having a charge opposite to that of said latent image; means for transferring the majority of said toner to a receiving layer to form a toner image; and means for removing residual toner from said photoreceptor; only said charging means being disposed between said developing means and said image transferring means so that prior to image transfer, the polarity of said toner is reversed and the surface of the photoreceptor is charged. 

1. In electrophotographic duplicating apparatus comprising a photoreceptor surface, charging means to charge said surface, exposing means to expose said charged surface, developing means to develop said charged surface and provide a toner image and toner image transfer means for transferring said toner image to a receiving material, the improvement wherein said toner transfer means is disposed immediately after said charging means, said charging means effecting the simultaneous functions of charging said photoreceptor and reversing the polarity of said toner image frOm an initial value, which initial value is opposite to the charge imparted by the charging means.
 2. The improvement as in claim 1 where there is only one said charging means.
 3. Electrophotographic duplication apparatus comprising: means for charging the surface of an electrophotographic photoreceptor; means for exposing the charged surface to form an electrostatically charged latent image thereon; means for developing said latent image with a toner having a charge opposite to that of said latent image; means for transferring the majority of said toner to a receiving layer to form a toner image; and means for removing residual toner from said photoreceptor; only said charging means being disposed between said developing means and said image transferring means so that prior to image transfer, the polarity of said toner is reversed and the surface of the photoreceptor is charged. 